I'll be the dissenter.
4 kids
1st 2 formula fed, after failed BF. Never CIO. AP'ed, but I didn't know there was a name for it.
Did not cosleep past the first few months, but they *never* complained about being in their cribs. Anyway, they slept GREAT! Great naps, Great nights, 12/13 hours, blah, blah, blah.
2nd 2, EBF.....they *never* sleep. #3 worse than #4. The baby will go to sleep w/o nursing, and is not nearly as fussy as #3 was, but she still doesn't sleep much more than 20 minute naps, and a very broken 8-10 hrs at night. I know some will say that's good sleeping, but I do not believe it is, based on prior experience. Especially when several hours of that wake time is spent with me bouncing/rocking/walking just trying to keep said babies from screaming their heads off. That says to me, that it's not enough.
Parenting is pretty much the same, except for the formula feeding for the first 2.
I do know that personality has a lot to do with it, but I am convinced that breastfeeding certainly has something to do with not sleeping. Maybe it's because my BF'd babes refuse a paci, and babies that take pacis sleep better? I suppose that's a theory, too.